1. Field of the Invention
The present invention relates to a photoelectric conversion device, and more particularly to an image sensor having a photoelectric conversion element and a color filter provided in a light detecting part thereof, on a substrate.
The present invention further relates to a multi-chip module type image sensor, a contact image sensor and an image reading apparatus, formed by arranging such image sensor by plural units in an array.
2. Related Background Art
As a line-type image reading device in the field of information processing system, instead of the prior reduction-type line sensor utilizing an optical system, developments are being made for an equal-size contact image sensor formed by mounting multiple semiconductor photosensors.
Also a color sensor is being recently desired instead of the prior monochromatic sensor.
For example, Japanese Patent Application Laid-open No. H03-289856 discloses a structure of such sensor. FIGS. 14 to 16 are equivalent circuit diagrams of an image sensor described in the above-mentioned patent reference. More specifically, FIG. 14 is a schematic view of a semiconductor image sensor of multi chip module type; FIG. 15 is a magnified view of a part A of the multi-chip module type semiconductor image sensor; and FIG. 16 is a view showing a configuration of an optical system utilizing the multi-chip module type semiconductor image sensor.
In FIGS. 14 and 16, there are shown an original 1, a circuit board 2 having desired circuits for mounting semiconductor image sensor, semiconductor image sensors S1 to Sn arranged in a linear array, a Celfoc lens array (trade name of Nippon Plate Glass Co.), and an original illuminating LED array 4. Also a combination of an LED and a light conducting member is often employed instead of the original illuminating LED array 4.
In FIG. 15, 5 indicates a light detecting aperture on the semiconductor image sensor. In case of a color sensor, the light detecting aperture 5 on the semiconductor image sensor is provided in three rows, which are respectively provided with red, green and blue color filters as shown in FIG. 15. The light detecting apertures of red, blue and green in a same column have respective outputs to constitute a color light detecting element. In order to facilitate formation of a color signal from the red, blue and green signals in a subsequent image processing, a pitch Q of the rows (a distance between centers of gravity of the light detecting apertures in a sub scanning direction) is selected same as or an integral multiple of a pitch P of the light detecting apertures in the main scanning direction. FIG. 15 shows a case where the row pitch Q is twice of the pitch P of the light detecting apertures in the main scanning direction (Q=2 P).
A peripheral circuit block 6 is provided on the semiconductor image sensor for controlling and outputting a photosignal, generated from the light received by the light detecting aperture.
Such semiconductor image sensor of multi chip module type has a feature capable of dispensing with a reduction optical system thereby enabling compactification, and is widely employed in an image processing apparatus such as a facsimile apparatus or a scanner.
However, in case the light detecting apertures in different rows having a same area as shown in FIG. 15, since the sensitivity is different for the respective colors depending on the light emission characteristics of LED, the spectral characteristics of the color filters and the spectral characteristics of the light detecting element, the image quality is determined by an output of a row corresponding to a color of lowest sensitivity.
In order to avoid such drawback, Japanese Patent Application Laid-open No. H11-150627 discloses changing the light detecting area of the pixel according to the transmittance of the color filter.
However the present inventor has found another drawback, in case of changing the light detecting area of the pixel, depending on the row of pixels (light detecting element row) in which the light detecting area is changed.